Dental implants are medical devices used to restore the function entailed with the loss of one or several teeth. To obtain successful function over long periods, the dental implants must be sufficiently anchored in the bone to withstand the forces induced by for example chewing. Two important factors for obtaining high anchorage strength are i) the chemical composition of the material and ii) the implant design at all length scales. Topographical features on different length scales induce for example nucleation sites for collagen and minerals, cell attachment and biomechanical stimulation necessary to prevent bone resorption and eventually to gain bone.
Dental implants commonly used today are made of titanium or titanium alloys with a screw shaped design and a rough surface.
There are to date several methods for treating metallic implants such as dental titanium implants in order to obtain a better attachment of the implant, and thus improved osseointegration. Some of these involve altering the morphology of the implant, for example by creating irregularities on the implant surface in order to increase the surface roughness in comparison to an untreated surface. It is believed that an increased surface roughness, which gives a larger contact and attachment area between the implant and the bone tissue, provides a better mechanical retention and strength between implant and bone. It is well-known within the art that a surface roughness can be provided by, for example, plasma spraying, blasting or acid etching.
Furthermore, it is known that osteoblasts, i.e, bone-forming cells, sense and react to multiple chemical and physical features of the underlying surface. Formation of bone at an implant surface requires the differentiation of precursor cells into secretory osteoblasts to produce unmineralised extracellular matrix (ECM), and the subsequent calcification of this matrix, as described in for instance Anselme K, Osteoblast adhesion on biomaterials, Biomaterials 21, 667-681 (2000).
Alteration of the chemical properties of the implant surface has frequently been used for achieving a better attachment of the implant to the bone tissue. Several methods involve the application of a layer of ceramic material, such as hydroxyapatite, on the implant surface in order to improve the bonding of the implant to bone since hydroxyapatite is chemically related to bone.
A common disadvantage with coatings comprising hydroxyapatite is, however, that they may be brittle and may flake or break off from the implant surface due to a stronger bond being formed between the bone and coating than between the coating and the implant, which may lead to an ultimate failure of the implant. Regarding the use of protein coatings, which have also been proposed, there are additional aspects to consider. Due to the chemical nature of proteins, a surface having a protein coating may require specific sterilization and storage conditions in order to maintain its biological activity. In addition, host tissue response (e.g. immunological response) to biomolecules such as proteins may be unpredictable.
Although various physical and chemical properties of implant surfaces are generally considered decisive factors for the biocompatibility of materials, the mechanism of new bone formation is still not known on a molecular level.
In brief, although there are many existing techniques for improving the osseointegration of an implant, there is a need for implants which offer further improved characteristics with respect to osseointegration and formation of a strong bone-implant attachment.